1. Technical Field
This invention relates generally to a strobe lighting system used in the capturing of for digital images.
2. Related Art
Digital cameras for capturing digital images are commercially available and allow individuals to create digital images, rather than images on film as with traditional cameras. In a digital camera, an image sensor measures reflected light from an object that is processed into a digital image.
Typically, digital cameras and other imaging products utilize image sensors (also known as electronic image sensors) that are solid-state devices. Examples of image sensors include charge-coupled device (CCD), charge injection devices (CID) and complementary metal oxide semiconductor (CMOS) imagers. The image sensors typically have a number of cells or pixels arranged along vertical and horizontal dimensions commonly referred to as a matrix (also known as a pixel array). Image sensors typically utilize off-chip signal processing to improve signal to noise (S/N) performance and compensate for reset noise. Image sensors may be found in various pixel array configurations, including SIF or QVGA 320×240, CIF 352×288, VGA 640×480, SVGA 800×600, XGA 1024×768, SxGA 1280×1024, 2 Mega pixel, 3 Mega pixel and 16 Mega pixels.
Image information sensed by each pixel of an image sensor is converted into a digital signal. The digital signal is created from the image information stored in the pixels of the pixel array and is output serial using an arrangement of shift registers (in the case of CCD) or via a row and column selection (in the case of CMOS imager). After the image information is converted into a digital signal referred to as image data, the image data is stored in a memory. The image data may be post processed by a digital signal processor (DSP) to improve the quality of the digital image.
An image sensor capable of capturing color images increase the complexity of processing the digital image data. In one approach, the image sensor has a geometric arrangement of cells forming a pixel responding to three primary colors, eg., red, green and blue. Since each cell senses a particular color, various algorithms are used to interpolate the missing color information. Alternately, two or more image sensors having different color sensitivity may be utilized and the image data combined by a signal processor.
When taking photographs with a traditional film camera, it is often desirable to have additional lighting to illuminate a subject. A “flash” is often utilized with a camera to provided illumination of the subject. Consequentially, problems exist when too much light or not enough light is reflected from the subject (also known as a object) onto the file. The problems of under exposure and over exposure result when too much light or too little light reach the film. Similar lighting problems exist with digital photography using an image sensor in place of film.
An image sensor utilized to capture an image has the same problems with subject lighting as traditional film cameras. A supplemental lighting source, such as a strobe, may be utilized with digital camera having an image sensor. The duration of the supplemental light is determined based on an average value of a preparatory image data. However, the amount of light generated does not correspond to a particular area of interest in the image. For example, in a portrait, the subject is typically placed in an area of interest in the center of the image; however, the supplemental light is generated based on the entire image, including the background. The light from the background behind the subject affects the calculation of the supplemental light in the same manner as the subject, and as such reduces the visual quality of the image. Therefore a system is needed to generate supplemental light that accords more weight to an area of interest of the image.